This invention relates to a sensorless controlling apparatus of a brushless motor for performing vector control by calculating the angle of a rotor using a d-axis current.
Generally, a controlling apparatus for performing vector control to control drive of a brushless motor is known. In the vector control, current values of three phases in a fixed coordinate system (namely, a coordinate system made up of a u axis, a v axis, and a w axis each forming an angle of 120 degrees and crossing at one point) are converted into currents of two phases (namely, d-axis current and q-axis current) in a rotating coordinate system (namely, a coordinate system made up of a d-axis indicating the magnetic flux direction of a field pole and a q-axis orthogonal to the d-axis) and the currents of two phases are used for controlling.
A sensorless controlling apparatus for performing the vector control and estimating the angle (position, phase) of a rotor without using a sensor for directly detecting the angle of a rotor of a brushless motor is known. As the sensorless controlling apparatus of a brushless motor, a controlling apparatus for estimating the angle of a rotor using the current values of a d-axis current and a q-axis current is disclosed. (For example, refer to Japanese Patent Laid-Open No. 2001-95281, Japanese Patent Laid-Open No. 2005-210813, Japanese Patent Laid-Open No. 2006-87152 and Japanese Patent Laid-Open No. 2007-53829)
However, in the related art described above, a motor model needs to be used to estimate the angle of the rotor of a brushless motor and the computation load is large. That is, since the angle of the rotor is estimated using inductance and resistance of a stator coil forming a part of the brushless motor, the computation load when loop processing is performed for frequently estimating the angle is large. Consequently, a high-cost CPU having a high-performance computation processing capability needs to be used; this is a problem.
Since the motor model of inductance, resistance, etc., of a coil forming a part of a brushless motor varies from one brushless motor to another, it is necessary to change a computation processing program to estimate the angle depending on the brushless motor to be controlled; this is a problem.